1. Field of the Invention
The present invention relates to a lithium ion capacitor, and more particularly, to a lithium ion capacitor having an anode active material layer including first active material particles and second active material particles disposed in pores between the first active material particles.
2. Description of the Related Art
In general, electrochemical energy storage devices are core parts of finished products, which are essentially used in all mobile information communication devices and electronic devices. In addition, the electrochemical energy storage devices will be used as high quality energy sources in new and renewable energy fields that can be applied to future electric vehicles and mobile electronic devices.
The electrochemical energy storage devices, typically, a lithium ion battery and an electrochemical capacitor, use an electrochemical theory.
Here, the lithium ion battery is an energy device that can be repeatedly charged and discharged using lithium ions, which has been researched as an important power source having higher energy density per unit weight or unit volume than the electrochemical capacitor. However, the lithium ion battery is difficult to be commercialized due to low stability, short use time, long charge time, and small output density.
In recent times, since the electrochemical capacitor has lower energy density but better instant output and longer lifespan than the lithium ion battery, the electrochemical capacitor is being rapidly risen as a new alternative that can substitute for the lithium ion battery.
In particular, a lithium ion capacitor among the electrochemical capacitors can increase energy density without reduction in output in comparison with other electrochemical capacitors, attracting many attentions.
However, since the energy density cannot be obtained while maintaining substantially the same output density as an electric double layer capacitor for commercialization, additional researches are still needed.
In recent times, while the lithium ion capacitor uses a large capacity of graphite in comparison with another active material to increase energy density, since a maximum theoretical capacity of the graphite is 372 mAh/g, increase in capacity of the anode is limited. Moreover, actually, it is impossible to completely use the maximum theoretical capacity of the graphite.